perf build: Default BUILD_BPF_SKEL, warn/disable for missing deps

LIBBPF is dependent on zlib so move the NO_ZLIB and feature check
early to avoid statically building when zlib is disabled. This avoids
a linkage failure with perf and static libbpf when zlib isn't
specified.

Move BUILD_BPF_SKEL logic to one place and if not defined set
BUILD_BPF_SKEL to 1. Detect dependencies of building with BPF
skeletons and warn/disable if the dependencies aren't present.

Change Makefile.perf to contain BPF skeleton logic dependent on the
Makefile.config result and refresh the comment about BUILD_BPF_SKEL.

Signed-off-by: Ian Rogers <irogers@google.com>
Tested-by: Namhyung Kim <namhyung@kernel.org>
Cc: James Clark <james.clark@arm.com>
Cc: Nick Terrell <terrelln@fb.com>
Cc: Patrice Duroux <patrice.duroux@gmail.com>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Kajol Jain <kjain@linux.ibm.com>
Cc: Athira Rajeev <atrajeev@linux.vnet.ibm.com>
Cc: Tiezhu Yang <yangtiezhu@loongson.cn>
Cc: Tom Rix <trix@redhat.com>
Cc: llvm@lists.linux.dev
Cc: bpf@vger.kernel.org
Link: https://lore.kernel.org/r/20230914211948.814999-3-irogers@google.com
Signed-off-by: Namhyung Kim <namhyung@kernel.org>

Author: captain5050

tools/perf/Makefile.config

@@ -216,12 +216,6 @@ ifeq ($(call get-executable,$(BISON)),)
   dummy := $(error Error: $(BISON) is missing on this system, please install it)
 endif
 
-ifeq ($(BUILD_BPF_SKEL),1)
-  ifeq ($(call get-executable,$(CLANG)),)
-    dummy := $(error $(CLANG) is missing on this system, please install it to be able to build with BUILD_BPF_SKEL=1)
-  endif
-endif
-
 ifneq ($(OUTPUT),)
   ifeq ($(shell expr $(shell $(BISON) --version | grep bison | sed -e 's/.\+ \([0-9]\+\).\([0-9]\+\).\([0-9]\+\)/\1\2\3/g') \>\= 371), 1)
     BISON_FILE_PREFIX_MAP := --file-prefix-map=$(OUTPUT)=
@@ -530,6 +524,16 @@ ifdef CORESIGHT
   endif
 endif
 
+ifndef NO_ZLIB
+  ifeq ($(feature-zlib), 1)
+    CFLAGS += -DHAVE_ZLIB_SUPPORT
+    EXTLIBS += -lz
+    $(call detected,CONFIG_ZLIB)
+  else
+    NO_ZLIB := 1
+  endif
+endif
+
 ifndef NO_LIBELF
   CFLAGS += -DHAVE_LIBELF_SUPPORT
   EXTLIBS += -lelf
@@ -571,22 +575,28 @@ ifndef NO_LIBELF
 
   ifndef NO_LIBBPF
     ifeq ($(feature-bpf), 1)
-      CFLAGS += -DHAVE_LIBBPF_SUPPORT
-      $(call detected,CONFIG_LIBBPF)
-
       # detecting libbpf without LIBBPF_DYNAMIC, so make VF=1 shows libbpf detection status
       $(call feature_check,libbpf)
 
       ifdef LIBBPF_DYNAMIC
         ifeq ($(feature-libbpf), 1)
           EXTLIBS += -lbpf
+          CFLAGS += -DHAVE_LIBBPF_SUPPORT
+          $(call detected,CONFIG_LIBBPF)
           $(call detected,CONFIG_LIBBPF_DYNAMIC)
         else
           dummy := $(error Error: No libbpf devel library found or older than v1.0, please install/update libbpf-devel);
         endif
       else
-        # Libbpf will be built as a static library from tools/lib/bpf.
-	LIBBPF_STATIC := 1
+        ifeq ($(NO_ZLIB), 1)
+          dummy := $(warning Warning: Statically building libbpf not possible as zlib is missing)
+          NO_LIBBPF := 1
+        else
+          # Libbpf will be built as a static library from tools/lib/bpf.
+          LIBBPF_STATIC := 1
+          $(call detected,CONFIG_LIBBPF)
+          CFLAGS += -DHAVE_LIBBPF_SUPPORT
+        endif
       endif
     endif
   endif # NO_LIBBPF
@@ -663,16 +673,36 @@ ifndef NO_LIBBPF
   endif
 endif
 
-ifdef BUILD_BPF_SKEL
-  $(call feature_check,clang-bpf-co-re)
-  ifeq ($(feature-clang-bpf-co-re), 0)
-    dummy := $(error Error: clang too old/not installed. Please install recent clang to build with BUILD_BPF_SKEL)
-  endif
+ifndef BUILD_BPF_SKEL
+  # BPF skeletons control a large number of perf features, by default
+  # they are enabled.
+  BUILD_BPF_SKEL := 1
+endif
+
+ifeq ($(BUILD_BPF_SKEL),1)
   ifeq ($(filter -DHAVE_LIBBPF_SUPPORT, $(CFLAGS)),)
-    dummy := $(error Error: BPF skeleton support requires libbpf)
+    dummy := $(warning Warning: Disabled BPF skeletons as libbpf is required)
+    BUILD_BPF_SKEL := 0
+  else ifeq ($(filter -DHAVE_LIBELF_SUPPORT, $(CFLAGS)),)
+    dummy := $(warning Warning: Disabled BPF skeletons as libelf is required by bpftool)
+    BUILD_BPF_SKEL := 0
+  else ifeq ($(filter -DHAVE_ZLIB_SUPPORT, $(CFLAGS)),)
+    dummy := $(warning Warning: Disabled BPF skeletons as zlib is required by bpftool)
+    BUILD_BPF_SKEL := 0
+  else ifeq ($(call get-executable,$(CLANG)),)
+    dummy := $(warning Warning: Disabled BPF skeletons as clang ($(CLANG)) is missing)
+    BUILD_BPF_SKEL := 0
+  else
+    $(call feature_check,clang-bpf-co-re)
+    ifeq ($(feature-clang-bpf-co-re), 0)
+      dummy := $(warning Warning: Disabled BPF skeletons as clang is too old)
+      BUILD_BPF_SKEL := 0
+    endif
+  endif
+  ifeq ($(BUILD_BPF_SKEL),1)
+    $(call detected,CONFIG_PERF_BPF_SKEL)
+    CFLAGS += -DHAVE_BPF_SKEL
   endif
-  $(call detected,CONFIG_PERF_BPF_SKEL)
-  CFLAGS += -DHAVE_BPF_SKEL
 endif
 
 ifndef GEN_VMLINUX_H
@@ -946,16 +976,6 @@ ifndef NO_DEMANGLE
   endif
 endif
 
-ifndef NO_ZLIB
-  ifeq ($(feature-zlib), 1)
-    CFLAGS += -DHAVE_ZLIB_SUPPORT
-    EXTLIBS += -lz
-    $(call detected,CONFIG_ZLIB)
-  else
-    NO_ZLIB := 1
-  endif
-endif
-
 ifndef NO_LZMA
   ifeq ($(feature-lzma), 1)
     CFLAGS += -DHAVE_LZMA_SUPPORT

tools/perf/Makefile.perf

@@ -120,7 +120,7 @@ include ../scripts/utilities.mak
 #
 # Define NO_LIBDEBUGINFOD if you do not want support debuginfod
 #
-# Define BUILD_BPF_SKEL to enable BPF skeletons
+# Set BUILD_BPF_SKEL to 0 to override BUILD_BPF_SKEL and not build BPF skeletons
 #
 # Define BUILD_NONDISTRO to enable building an linking against libbfd and
 # libiberty distribution license incompatible libraries.
@@ -1042,7 +1042,7 @@ SKELETONS += $(SKEL_OUT)/augmented_raw_syscalls.skel.h
 $(SKEL_TMP_OUT) $(LIBAPI_OUTPUT) $(LIBBPF_OUTPUT) $(LIBPERF_OUTPUT) $(LIBSUBCMD_OUTPUT) $(LIBSYMBOL_OUTPUT):
 	$(Q)$(MKDIR) -p $@
 
-ifdef BUILD_BPF_SKEL
+ifeq ($(CONFIG_PERF_BPF_SKEL),y)
 BPFTOOL := $(SKEL_TMP_OUT)/bootstrap/bpftool
 # Get Clang's default includes on this system, as opposed to those seen by
 # '--target=bpf'. This fixes "missing" files on some architectures/distros,
@@ -1120,11 +1120,11 @@ bpf-skel: $(SKELETONS)
 
 .PRECIOUS: $(SKEL_TMP_OUT)/%.bpf.o
 
-else # BUILD_BPF_SKEL
+else # CONFIG_PERF_BPF_SKEL
 
 bpf-skel:
 
-endif # BUILD_BPF_SKEL
+endif # CONFIG_PERF_BPF_SKEL
 
 bpf-skel-clean:
 	$(call QUIET_CLEAN, bpf-skel) $(RM) -r $(SKEL_TMP_OUT) $(SKELETONS)